The present invention relates generally to the concept of airplanes having folding winglets, and more particularly, to winglet assemblies which can be extended during cruise to increase span and automatically/passively retracted to an upright position as needed to reduce the wing bending moment and aircraft weight when subjected to large loads at conditions such as dive.
Because of the reduced size of the flight deck and reduced hangar space, it has long been known to fold the wings of fighter aircraft when stored onboard aircraft carriers. Such aircraft normally include a power driven actuator system which functions to move an outboard portion of the aircraft wing between an extended position suitable for flight and a retracted storage position. U.S. Pat. No. 5,310,138 entitled "Wing Fold Actuator System for Aircraft" issued May 1994 to Thomas F. Fitzgibbon is believed to be typical of such an aircraft. It is noted that the actuator system is provided to pivot the wing from a folded position when stored to an extended position prior to flight. The disclosure of the '138 patent is herein incorporated by reference. There is no suggestion in the '138 patent of pivoting the wing between deployed and retracted positions during operation of the aircraft.
It is known that having an aircraft's winglets extend at an angle to the remaining portion of the wing can affect the flight characteristic of the aircraft. U.S. Pat. No. 5,072,894 entitled "Apparatus and Method for Increasing the Angle of Attack Operating Range of an Aircraft" issued December 1991 to Daniel R. Cichy, the disclosure of which is herein incorporated by reference, teaches that the by employing vertically downwardly extending tip fins, it is possible to increase the angle of attack operating range of an aircraft. At high angles of attack, the tip fins extend approximately 90.degree. to the inboard portion of the wing. There is no suggestion of raising the tip fins above the wing nor is there any suggestion of extending the tip fins during flight.
Commercial aircraft have been known to employ foldable wing tips which can be raised to reduce the landing space occupied by the aircraft. By raising the wing tips, aircraft having large wings, such as the Boeing 777, can reach current loading gates that would otherwise be unavailable. A latching mechanism for locking the wing tips in their upright position when on the ground is taught in U.S. Pat. No. 5,427,329 entitled "Locking Hydraulic Latch Pin Actuator" issued June 1995 to Michael E. Renzelmann et al, the disclosure of which is herein incorporated by reference. A hydraulic actuator is employed to move the primary lock member between locked and unlocked positions when the aircraft is on the ground. There is no suggestion in the '329 patent that the wing tips are movable when the aircraft is in flight.
None of the cited patents employs a wing including a foldable winglet that can be folded while the aircraft is in flight. As a result, none of the cited patents can take advantage of the extended winglets during cruise and folded winglets during more severe load conditions.
The present invention overcomes the size and structural weight problems associated with a large span while retaining the reduced drag benefit of a large span during cruise.